Cathodoluminescent image displays are known in the art. In these displays high energy electrons are directed at a cathodoluminescent material (phosphor) wherein some of the energy of the electrons is converted to photon energy some of which is emitted from the display. The energy conversion process is inefficient resulting in 80% or more of the energy of the impinging electrons being converted to heat energy in the phosphor.
The brightness, or luminous output, of a display is, in addition to other parameters, generally proportional to the density of electrons incident at the phosphor. That is, luminous output increases as current density increases. Many display applications require high brightness which correspondingly demands increased current density to the phosphor. The required high current density will also result in high heat energy density in the phosphor and immediate material on which the phosphor resides. Since the phosphor and faceplate materials are effective insulators they serve as relatively poor conductors of thermal energy. Unacceptably high temperatures may result which can severely degrade device performance due to thermal quenching of the phosphor material or physical damage to the device structure caused by stress induced failure. Further, since displays typically, are not uniformly illuminated, local hot spots due to high brightness local regions of illumination, may result.
One method of the prior art to reduce the temperature at the phosphor and photon emission region of the cathodoluminescent display is through the use of cooling fans to rapidly remove heat from the display. Cooling fans are unsuitable in some applications due to size, power, noise, and cooling capacity constraints.
A second method of the prior art to reduce the temperature at the phosphor and photon emission region of the cathodoluminescent display is through the use of convection cooling techniques and is depicted in FIG. 1. In this method a volume of liquid is disposed in contact with the display at the area of high thermal energy flux. Convection flow is utilized to carry the unwanted heat away from the display structure. The liquid medium must be held in a containment vessel and the containment vessel must be sealed and rigidly held in position with respect to the display surface. This cooling method may introduce unacceptable distortions to the image, which must traverse the extent of the cooling medium, because of the motion of the medium.
Therefore, a need exists to provide a method and/or a display apparatus to overcome at least some of these shortcomings of the prior art.